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Study Onasymmetric Syntheses of Opticallyactive α-(2-Methyl-3-furylthio) Ketones

Author: YuJieFei
Tutor: TianHongYu
School: Beijing Technology and Business University
Course: Applied Chemistry
Keywords: Chiral spices α-(2 - methyl-3 - furyl thio ) ketone α-hydroxy- ketone Silyl enol ethers Shiyi An asymmetric epoxidation
CLC: O621.34
Type: Master's thesis
Year: 2010
Downloads: 36
Quote: 0
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Abstract


This thesis method by Shiyi An asymmetric the epoxidized preparation of optically active α-(2 - methyl-3 - furyl thio) ketones perfume compounds. The thesis two preparation of α-(2 - methyl-3 - furyl thio) ketones racemic different methods. The first method to bromoalkanes as raw materials, by the Grignard reaction, Swern oxidation, the halogen-substituted and nucleophilic substitution of four-step reaction of α-(2 - methyl-3 - furyl thio) ketones. First the bromoalkanes with ethyl through Grignard reaction, an alcohol, and about 85% yield; alcohol by Swern oxidation to give the ketone, about 75% yield; obtained ketone reaction with the liquid bromine to give the corresponding α-bromo substituting ketone, about 70% yield; α-bromoketone under the action of potassium carbonate and 2 - methyl-3 - furanthiol reaction to obtain the final product of α-(2 - methyl-3 - furyl thio) ketone, about 65% yield. The final product in through 1 HNMR 13 CNMR and MS were characterized. Route total yield of about 30% of the yield. And literature from the corresponding α-chloroketone in methanol and sodium compared to a synthetic method of 2 - methyl -3 - furan thiol, the route operation easier, and the yield is higher. The second approach to the ketone compound as a starting material through enolate, oxidation and nucleophilic substitution reaction to give the product. First reaction first with trimethylchlorosilane ketone under alkaline conditions to give the silyl enol ether, 4 - (3 - heptene-yl) trimethyl silyl enol ether and 5 - (4 - nonene-yl) trimethylammonium The silyl enol ether yields were above 80%, a 2,6 - dimethyl-4 - (3 - heptene-yl) trimethyl silyl enol ether is slightly lower, by approximately 70%. Silyl enol ether with m-chloroperoxybenzoic acid oxidation, α-hydroxy-ketone, the production rate of more than 85%. α-hydroxy-ketone, the reaction with methanesulfonyl chloride, the hydroxy into mesylate, to give the corresponding mesylate, the production rate of about 90%. Then methanesulfonate with 2 - methyl-3 - furyl thiol under basic conditions to give α-(2 - methyl-3 - furyl thio) ketones fragrance compound in a yield of 82-85% between. This method is compared with the literature methods, through the silyl enol ether to the preparation of α-hydroxy ketones, and does not exist polyhydric substituted, and the α-hydroxy ketone is converted to mesylate, methanesulfonate is a good from leaving group, compared with the α-halo ketone high activity, more easily with 2 - methyl -3 - furanthiol nucleophilic substitution reaction to obtain product. The synthetic method is no other reported in the literature, with the advantages of simple, fewer side effects and high yield. The ketone converted to the silyl enol ether, and then by Shiyi An asymmetric epoxidation to obtain optically active α-hydroxy-ketone. This paper investigated on the silicon of the silyl enol ether substituent group and the amount of catalyst, reaction temperature Shiyi An asymmetric epoxidation of. Key factor, the amount of catalyst, and the reaction temperature on the reaction of the chemical yield and selectivity effects are not obvious, and the silyl enol ether double bond and the substituent on the silicon group is to determine the reaction of the group of large steric conducive reactive chemical yield and selectivity improved. 3 - hydroxy-4 - heptanone highest yield up to 75% ee values ​​up to about 61%; 4 - hydroxy-5 - the nonanone chemical yield up to 80% ee values ​​up to 50% around; 2,6 - dimethyl-3 - hydroxy-4 - heptanone yield up to about 80% ee value can reach up to about 84%. Sharpless Asymmetric Dihydroxylation product according to the literature, by comparison, to confirm that the obtained product is mainly in the R configuration. The obtained optically active α-hydroxy ketone to hydroxy group is converted to a mesylate by SN2 nucleophilic substitution reaction to obtain an optically active target product of 3 - (2 - methyl-3 - furyl thio) -4 - heptyl one, 4 - (2 - methyl - 3 - furyl thio) -5 - nonanone and 2,6 - dimethyl - 3 - (2 - methyl-3 - furyl thio) -4 - heptanone ee value of the product was 55.8%, 44.6%, 77.6%, respectively. The final ee value of the product with the intermediate α-hydroxy ketone is very close, indicating that the nucleophilic substitution reaction, substantially no racemization was occurred.

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CLC: > Mathematical sciences and chemical > Chemistry > Organic Chemistry > Organic Chemistry general issues > Synthetic organic chemistry > Asymmetric Organic Synthesis
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